1. Field of the Invention
The present invention relates to a column base fitting having a lower end of a column member of a construction structure fitted thereon and screwed with a top end of an anchor bolt protruding upward from in a base concrete, and a column base structure using it.
2. Description of the Conventional Art
FIGS. 28 and 29 are reference views explanting a first conventional column base fitting 6 and a first conventional column base structure 2 using it.
As illustrated in FIG. 28, the first conventional column base structure 2 includes a plate-shaped column base fitting 6, on which the lower end surface of a steel column 4 (column member) is jointed on the upper surface thereof by welding. The column base fitting 6 is provided on a base concrete 3 through a mortar 8.
An top end of an anchor bolt 10 penetrating the mortar 8 and protruding upward from in the base concrete 3, is inserted in bolt insertion holes 6a and 6b (refer to FIG. 29) of the column base fitting 6, and a female screw of a nut member 12 is screwed with a male screw formed on the anchor bolt 10. In such a way, the steel column 4 is stood and fixed on the base concrete 3 through the column base fitting 6 (for example, refer to Japanese Patent No. 4006503).
In addition, in the conventional column base structures, for example, Japanese Patent Application Laid-Open No. 2003-336266 discloses the column base structure including a column base fitting which includes a bottom plate and a support base. The support base is structured such that the center of an upper surface of the bottom plate protrudes upward higher than the periphery of the bottom plate, and a lower end surface of the steel column is jointed on an upper surface of the support base by welding.
In the column base structure according to the Japanese Patent Application Laid-Open No. 2003-336266, the top end of the anchor bolt penetrating the mortar from in the concrete base and protruding upward, is inserted in a bolt insertion hole formed in the thickness direction of the periphery portion of the bottom plate of the column base fitting. A male screw formed on the anchor bolt screws with a female screw of the nut member. In such a way, the steel column is stood and fixed on the base concrete through the column base fitting.
The column base fitting 6 in the first conventional column base structure is formed to be a plate shape having a metal square shape, both surfaces of upper and lower, and thickness, as illustrated in FIG. 29. The bolt insertion holes 6a and 6b are formed in total 12 holes. These bolt insertion holes 6a and 6b penetrate in the thickness direction of the plate shape (in the figure, the perpendicular direction to the drawing paper) and are formed to have an approximately same diameter respectively. One anchor bolt 10 is loosely inserted in each hole.
The bolt insertion hole 6a of the column base fitting 6 is formed at each four corner portions of the square shape of the column base fitting 6 one by one. Namely, each center position of the four bolt insertion holes 6a in the column base fitting 6 is located in parallel direction to two sides extending in the lateral direction in FIG. 29 and at a position apart by a length L1 from an imaginary line X in the vertical direction in the figure. The imaginary line X passes a center position of the column base fitting 6. Further, each center position of the four bolt insertion holes 6a in the column base fitting 6 is located in parallel direction to two sides extending in vertical direction in the figure and at a position apart by a length L1 from an imaginary line Y in the lateral direction. The imaginary line Y passes a center position of the column base fitting 6.
Each center position of the bolt insertion holes 6b in the column base fitting 6 is located at an equivalent position in the length direction between the bolt insertion holes 6a and 6a, which are both ends of each four sides of the square shape of the column base fitting 6. In other words, the center position of the bolt insertion hole 6b in the column base fitting 6 is located at two positions which trisect the line connecting the each center of the bolt insertion holes of 6a and 6a. 
The center position of the bolt insertion hole 6b is located, for example, at a position apart by a length L1 from the imaginary line Y in the lateral direction in the figure in two sides extending in the vertical direction in FIG. 29. Further, the center position of the bolt insertion hole 6b is located at a position apart by a length L2 from the imaginary line X in the vertical direction in FIG. 29. The length L2 is the trisected length of L1. In two sides extending in the lateral direction in FIG. 29, the bolt insertion hole 6b is located in the position in the same length.